What Causes White Squiggly Lines on My Tomato Plant Leaves?

Excessive pesticide use can lead to insect infestations on tomato plants.

Finding white squiggly lines on your tomato plant leaves is a sure sign that leafminers are infesting your garden. Hardy in U.S. Department of Agriculture plant hardiness zones 10 and 11, tomato plants (Lycopersicon esculentum) -- which are often grown as an annual -- make the ideal meal for various insects such as leafminers. Controlling these annoying and potentially damaging pests requires a combination of cultural and chemical treatments used in conjunction with one another.

Know Your Enemy

The adult stage of leafminers are small yellow and black flies that insert their eggs into the leaves of plants. After hatching, the larvae of leafminers feed between the leaf surfaces, resulting in the white squiggly lines you found on your tomato plant leaves. Once the larva matures, it drops to the ground where it pupates. The entire life cycle of the leafminer can take two weeks if the weather is warm, and up to ten generations can occur in one year.

Control Leafminers Naturally

Natural enemies of the leafminers -- such as the parasitic wasps Diglyphus begini and Chrysocharis parksi -- naturally keep the worms under control. Planting flowers that are known to attract beneficial insects will increase the number of predators in your garden. For example, Queen Anne’s lace (Daucus carota) -- which grows in U.S. Department of Agriculture plant hardiness zones 4 through 9 -- attracts parasitic wasps that feed on the larval stage of leafminers.

Insecticides May Help

Leafminers are resistant to several common insecticides including pyrethroids and carbamates, according to the University of California Statewide Integrated Pest Management Program website. Using these insecticides will cause the leafminers’ numbers to increase. It is suggested, instead, to use cyromazine, abamectin or spinosad insecticides to control these annoying pests. Since each type of insecticide for leafminer control has directions designed specifically for that chemical, refer to the label on the bottle for proper application instructions. For example, one brand of cyromazine insecticide calls for diluting 2.66 ounces of the chemical in 10 gallons of water and applying as a foliar spray to tomato plants. Repeated applications at seven-day intervals may be required to maintain control of leafminers.

Considerations and Precautions

Prevent an infestation by only planting pest-free seedlings, and destroy any infested tomato plants before transplanting. Also, consider planting tomato varieties that are less susceptible to leafminers such as cultivar VF 145. Ensuring the tomato plants are healthy and not under water stress helps infested plants recover from a leafminer infestation. Also, keep the area free of weeds, which can attract leafminers.

About the Author

Marylee Gowans has written about gardening for both online and print publications. She attended the University of Akron, graduating with a Master of Fine Arts in creative writing. In 2009, she received master gardener certification from the Master Gardeners of Summit County, Ohio.